1. Field of the Invention
The present invention relates to an imaging apparatus including a cooling function and a dew condensation prevention function of an imaging device.
2. Description of the Related Art
Conventionally, according to an imaging apparatus for imaging by using a solid-state imaging device, it has been known that an image is deteriorated as a temperature of the solid-state imaging device becomes higher.
Therefore, in the case of using such a solid-state imaging device, an imaging device is entirely cooled in order to prevent the temperature of the solid-state imaging device from being increased. As cooling means for this purpose, for example, a Peltier element has been known.
FIG. 1 shows a conventional imaging apparatus including a cooling structure using a Peltier element.
In FIG. 1, a solid-state imaging device 41 for imaging an image has a Peltier element 42. The Peltier element 42 serves as an element for cooling the solid-state imaging device 41, and its COOL surface is closely attached to the solid-state imaging device 41 and its HOT surface is closely attached to a surface of a base 43a of an exterior unit 43, respectively.
The exterior unit 43 has the base 43a and an exterior cover 43b. The exterior cover 43b is provided so as to cover the periphery of the solid-state imaging device 41. The exterior cover 43b has a window unit 43e with opposed to the imaging surface of the solid-state imaging device 41. The exterior cover 43b is attached on the base 43a in airtight by a screw 43c with a packing 43d interposed therebetween. A cover glass 44 is disposed at the window unit 43e of the exterior cover 43b. The cover glass 44 adheres to the window unit 43e in airtight by means of an adhesive agent or the like. The lead wires 45 and 46 are connected to the solid-state imaging device 41 and the Peltier element 42, respectively. The lead wires 45 and 46 are guided to the outside penetrating through the base 43a of the exterior unit 43, and are connected to a power source (not shown) or the like. The base 43a through which the lead wires 45 and 46 penetrate are sealed by injecting a silicon resin or the like therein so as to prevent air from moving in and out. A silica gel 47 dries a space that is sealed by the exterior cover 43b including the solid-state imaging device 41.
According to the imaging apparatus configured as described above, the solid-state imaging device 41, of which temperature rises upon imaging, is cooled by the Peltier element 42. The Peltier element 42 radiates heat that is absorbed from the solid-state imaging device 41 to the exterior unit 43, and further, the exterior unit 43 radiates the heat to air.
However, the exterior unit 43 radiates the heat to air and simultaneously, also radiates the heat to an inner space of the exterior cover 43b including the solid-state imaging device 41. Therefore, the inside of the exterior cover 43b also rises in temperature, and as a result, an internal circulation of heat is generated to increase a temperature of the solid-state imaging device 41.
Cooling of the solid-state imaging device 41 is simply represented by the following expression.
Amount of cooling of solid-state imaging device (W)=amount of heat radiation to air−amount of internal circulation of heat
As being obvious from this expression, for example, as shown in FIG. 2, Peltier output by the Peltier element 42 is increased, and as shown in FIG. 2A, a cooling temperature of the solid-state imaging device 41 is increased. As a result, the temperature of the exterior unit 43 is increased, and as shown in FIG. 2B, an amount of heat radiation to air is increased. However, as shown in FIG. 2C, an amount of internal circulation of heat within the exterior cover 43b is also increased, so that a cooling efficiency is deteriorated. If the Peltier output is further increased from this state, a difference ΔW between the amount of heat radiation to air and the amount of internal circulation of heat is saturated, and the cooling temperature of the solid-state imaging device 41 is also saturated.
Therefore, for example, technologies disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-211823 and Jpn. UM Appln. KOKOKU Publication No. 5-46381, respectively, are known.
FIG. 3 is a diagram showing a schematic configuration of an imaging apparatus disclosed in Jpn. Pat. Appln. KOKAI Publication No. 7-211823. In FIG. 3, the same parts as FIG. 1 are given the same reference numerals.
As shown in FIG. 3, a COOL surface of a second Peltier element 51 is closely attached to the outside surface of the base 43a of the exterior unit 43. On a HOT surface of the second Peltier element 51, a cooling wheel 52 is closely attached. Between the cooling wheel 52 and the outside surface of the base 43a, a heat insulator 53 is arranged so as to surround the second Peltier element 51. The base 43a, the heat insulator 53, and the cooling wheel 52 are fixed in one portion by a fixing screw 54. A lead wire 55 is connected to the second Peltier element 51.
According to such a configuration, it is possible to further radiate a portion of the heat radiation from the solid-state imaging device 41 to the exterior unit 43 via the Peltier element 42 to the cooling wheel 52.
Movement of heat in this case can be represented by the following expression.
Amount of cooling of solid-state imaging device (W)=amount of heat radiation to outside by cooling wheel+amount of heat radiation to outside by exterior unit−internal circulation of heat
Thereby, as the solid-state imaging device 41 is intensively cooled (output to the Peltier element 42 is increased), increasing amount of heat radiation to the cooling wheel 52 by the second Peltier element 51 and making the heat radiation by the exterior unit 43 even, the internal circulation of the heat is decreased. Thereby, a cooling efficiency of the solid-state imaging device 41 is improved so as to increase a cooling temperature.
On the other hand, FIG. 4 is a block schematic view of an imaging apparatus disclosed in Jpn. UM Appln. KOKOKU Publication No. 5-46381. In FIG. 4, the same parts as FIG. 1 are given the same reference numerals.
As shown in FIG. 4, a heat insulator 61 is disposed on the inside surface of the base 43a of the exterior unit 43 and the inside surface of the exterior cover 43b of the exterior unit 43.
According to such a configuration, due to a heat insulation effectiveness of the added heat insulator 61, a heat radiation amount to the inside of the exterior unit 43 can be decreased, and thereby, the internal circulation of the heat can be decreased. As a result, improving the cooling efficiency of the imaging device 41, the cooling temperature can be also increased.